Scientists conservatively estimate there are about 10,000,000,000,000,000 planets in the universe that can be seen by our telescopes. Ten million billion planets. And that's only what can be seen, the actual number is probably a lot higher.
Even if it's very rare that planets support life and we assume only 1 in a million planets can, that's still 10 billion planets capable of producing life.
All stars start in the same way, with a bunch of hydrogen and helium left over, the two most common abundant materials in space and the basis of all llife as we know it. With this process repeated over and over again billions of times it's only reasonable to expect that many planets have lots of similar characteristics, and could support some form of life.